This application is related to Japanese Patent Application Nos. 2002-122963 filed on Apr. 24, 2002 and 2002-236057 filed on Aug. 13, 2002, whose priorities are claimed under 35 USC xc2xa7119, the disclosure of which is incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to an apparatus for forming a fluorescent layer in a plasma display panel and, more particularly, to a fluorescent layer forming apparatus including an improved nozzle.
2. Description of the Related Art
A conventional fluorescent layer forming apparatus disclosed in Japanese Unexamined Patent Publication No. H11-204032 (1999) will be described with reference to FIGS. 13, 14(A) and 14(B). The conventional fluorescent layer forming apparatus includes a dispenser 201 which has a plurality of ejection ports generally linearly arranged at predetermined intervals. In a fluorescent layer forming process employing the conventional fluorescent layer forming apparatus, as shown in FIG. 13, a fluorescent material paste 207 prepared by dispersing fluorescent particles in a liquid medium is ejected from the dispenser 201 through a mask 226 into linear recesses defined between plural barrier ribs 224 arranged parallel to each other on a rear substrate 220, and heat-treated for formation of fluorescent layers 225. As shown in FIGS. 14(A) and 14(B), the dispenser 201 includes fine rod-shaped guides 221 which respectively project from the ejection ports generally centrally of the ejection ports. The fluorescent material paste 207 is ejected along the guides 221, while the dispenser 201 is moved relative to the substrate 220. Thus, the fluorescent layers 225 are formed in the linear recesses between the barrier ribs 224.
In the conventional fluorescent layer forming apparatus, the fluorescent material paste which has a high viscosity and a low surface tension unlike water is attracted to the guides 221 and falls vertically downward. Where the guides 221 are each composed of a hair or a polyamide filament, the fluorescent material paste can be ejected with the guides 221 kept in contact with the bottoms of the recesses. Thus, the conventional fluorescent layer forming apparatus can assuredly apply the fluorescent material paste into the recesses.
In the conventional fluorescent layer forming apparatus having the aforesaid construction, the fluorescent material paste is simply ejected along the guides from the ejection ports. At this time, the fluorescent material paste is liable to clot around the guides to form relatively large clots, depending on the viscosity of the fluorescent material paste. As a result, the fluorescent material paste is likely to adhere onto top edges of the barrier ribs or to enter recesses adjacent to the intended recesses (thereby to be mixed in different color fluorescent material pastes applied in the adjacent recesses). Thus, the conventional fluorescent layer forming apparatus fails to accurately form the fluorescent layers.
To overcome the aforesaid drawback, the present invention is directed to a fluorescent layer forming apparatus which is capable of accurately forming a fluorescent layer without formation of a relatively large clot of a fluorescent material paste.
In accordance with one aspect of the present invention, there is provided a fluorescent layer forming apparatus for applying a fluorescent material paste into a recess defined between barrier ribs formed on a substrate for formation of a fluorescent layer in a plasma display panel production process, the apparatus comprising: a nozzle for ejecting the fluorescent material paste; and a plurality of fine attachments provided at one end of the nozzle with distal end portions thereof being arranged in convergent relation, whereby the fluorescent material paste is ejected along the plurality of fine attachments so as to be applied onto a predetermined position in the recess for the formation of the fluorescent layer. According to this inventive aspect, proximal ends of the fine attachments are fixed to the nozzle, and the distal ends of the fine attachments are arranged in convergent relation. When the fluorescent material paste is supplied into the nozzle, the front of the fluorescent material paste moves along the plurality of fine attachments arranged in convergent relation. Therefore, the fluorescent material paste is convergently retained between the fine attachments and ejected from the nozzle without formation of a clot. Hence, the fluorescent layer can accurately be formed in the intended recess defined between the barrier ribs without adhesion thereof onto the top edges of the barrier ribs.
In accordance with the present invention, the fine attachments are adapted to control the eject line of the fluorescent material paste for guiding the fluorescent material paste to a predetermined position in the recess.
Specific example of the material for the fine attachments includes stainless.
The inventive fluorescent layer forming apparatus may be adapted to eject the fluorescent material paste with the distal ends of the fine attachments kept in contact with the bottom of the recess defined between the barrier ribs. In this case, the nozzle is scanned for the application of the fluorescent material paste, while the distal ends of the fine attachments fixed to the nozzle are kept in contact with the bottom of the recess. Therefore, the fluorescent material paste is guided along the fine attachments into the recess between the barrier ribs. Thus, the fluorescent layer can more accurately be formed in the intended recess between the barrier ribs.
In the inventive fluorescent layer forming apparatus, the fine attachments may each be composed of a material having a wetting contact angle of not greater than 60 degrees with respect to the fluorescent material paste. In this case, the fluorescent material paste supplied to the nozzle smoothly moves along the fine attachments composed of the material having a wetting contact angle of not greater than 60 degrees with respect to the fluorescent material paste without stagnation, and is ejected at a predetermined ejection rate from the nozzle without formation of a clot. As a result, the fluorescent layer thus formed has a uniform thickness.
In the inventive fluorescent layer forming apparatus, the fluorescent material paste may have a viscosity of 5 Paxc2x7s to 50 Paxc2x7s at a sheer rate of 4 sxe2x88x921. In accordance with the present invention, the term xe2x80x9csheer ratexe2x80x9d refers to a velocity gradient of a flux of the fluorescent material paste. More specifically, it refers to a velocity gradient determined by a flux of the fluorescent material past being ejected from the nozzle and a flux of the fluorescent material paste retained in a retaining portion of the nozzle at a position from the center line of the nozzle a predetermined distance.
An appropriate value of the viscosity of the fluorescent material paste can be determined in accordance with Hagen-Poiseuille""s formula using the inner diameter of the nozzle, the amount of the fluorescent material paste to be ejected, the pressure under which the fluorescent material paste is to be ejected and the like as parameters. In this case, the fluorescent material paste having a viscosity of 5 Paxc2x7s to 50 Paxc2x7s at a sheer rate of 4 sxe2x88x921 is supplied to the nozzle and, therefore, smoothly moves along the fine attachments without stagnation and is ejected at a predetermined ejection rate from the nozzle without formation of a clot. As a result, the fluorescent layer thus formed has a uniform thickness.
In accordance with another aspect of the present invention, there is provided a fluorescent layer forming apparatus for applying a fluorescent material paste into a recess defined between barrier ribs formed on a substrate for formation of a fluorescent layer in a plasma display panel production process, the apparatus comprising: a nozzle for ejecting the fluorescent material paste; and a plurality of fine attachments provided at one end of the nozzle as projecting from the nozzle; wherein portions of the fine attachments projecting from the nozzle each have a length not smaller than the radius of the nozzle. According to this inventive aspect, the portions of the fine attachments projecting from the nozzle each have a length not smaller than the radius of the nozzle, so that the fluorescent material paste can smoothly and accurately be applied dropwise into the recess without deflection thereof around the outer periphery of the fine attachments. Therefore, the fluorescent material paste can smoothly be applied dropwise into the recess continuously for a long period of time.
In accordance with further another aspect of the present invention, there is provided a fluorescent layer forming apparatus for applying a fluorescent material paste into a recess defined between barrier ribs formed on a substrate for formation of a fluorescent layer in a plasma display panel production process, the apparatus comprising: a nozzle having an outlet for ejecting the fluorescent material paste; and a plurality of fine attachments provided at one end of the nozzle, the fine attachments defining a retention portion having a greater cross sectional area than the outlet of the nozzle and an ejection port having a smaller cross sectional area than the retention portion. According to this inventive aspect, the retention portion having a greater cross sectional area than the outlet of the nozzle and the ejection port having a smaller cross sectional area than the retention portion are defined by the fine attachments fixed to the end of the nozzle. Therefore, the fluorescent material paste can accurately be applied into the recess. Since the fluorescent material paste is once retained in the retention portion and then ejected, the fluorescent material paste can smoothly be supplied even if the ejection rate of the fluorescent material paste is changed.
The inventive fluorescent layer forming apparatus may further comprise a filter provided above a fluorescent material paste supply port of the nozzle, wherein proximal ends of the fine attachments are fixed to the filter. In this case, the filter provided above the fluorescent material paste supply port of the nozzle has a predetermined mesh size, so that particles greater in size than the predetermined mesh size can be filtered out for prevention of clogging of the nozzle before the fluorescent material paste is supplied into the nozzle. Thus, stable formation of the fluorescent layer can be ensured for a long period of time.